The present invention relates to a method for grinding railroad wheels, and more particularly, a method for the sprue removal and finish grinding of cast steel railroad wheels.
The preferred method for manufacturing cast steel railroad wheels is the bottom pressure casting foundry operation wherein molten steel under pressure is forced upwardly into a graphite mold and filled from the bottom upwardly. This bottom pressure casting operation eliminates many of the concerns associated with traditional top pouring molten steel in foundry operations such as splashing and insufficient filling of molds. In the casting of railroad wheels, it is usual for the front side of the wheel, which also corresponds with the top half of the mold, to have a raised center hub portion and, depending on the size of the wheel, from 6 to 14 raised sections or sprues extending from the plate portion of the wheel near the rim. The raised hub area and the raised sprue areas extending from the plate are remnants of risers that are designed to hold additional metal to be available to fill downwardly into the mold during the cooling and solidification of the wheel just after pouring. The center raised hub section is removed during the flame cutting of the axle hub, which is later finished by a hub-boring operation. The sprues are difficult to remove and would require considerable effort if removed by normal-sized, hand-held grinders. In fact, such hand-held grinding operation is not currently used in present wheel-making operations. The current method for removal of such sprues is a so-called sprue washing operation which amounts to a carbon arc melting of the raised sprue. A hollow electrode is utilized to electrically melt the sprue with air blown through the hollow portion of the electrode to blow away the molten metal. This operation is like carbon arc welding but with no material depositing. However, removed molten metal is deposited on adjacent sections of the wheel which requires subsequent chipping away which is a time consuming and difficult process. Further, the sprue washing operation is not a desirable work area as the operators must wear a protective suit with a separate airhood supply and adequate noise protection.
After such sprue washing and chipping operations are completed, the cast steel wheel must be heat treated by raising its temperature, allowing it to cool, cleaning the wheel by a shot-blast operation, and then finish grinding the surface areas from which the sprues were removed. Such finish grinding is a typical hand-grinding operation and again a difficult process for the operator.
Machine grinding of ingots and billets are known in the steel industry. Typically, such operation amounts to scarfing of the ingot's surface to remove minor cracks or surface imperfections after the ingot has cooled, although certain scarfing operations are preferred when the ingot is at an elevated temperature. Applicants are not aware of any operation wherein sprues are removed from cast steel railroad wheels when the wheel has just solidified from the initial casting operation.